Composite electrode



jun@ 2?, w67 D. R RsFFx-I COMPOSITE ELECTRODE Filed Oct. 50, 19525INVENTOR United Statesl Patent T Westinga corpora- This inventionrelates to the storage of electrical energy and in particular concernsnovel composite electrodes and secondary cells and batteries thatinclude at least one of the composite electrodes as an importantelement.

It is a primary object of the present invention to provide a compositeelectrode for use in secondary cells and storage batteries that iseasily prepared from readily available materials, that eliminates partsheretofore necessary and makes possible other simplifications in cellsand batteries with which the new electrode may be used.

A further object of the invention is to provide a cornposite electrodeto retain bromine in a zinc bromide cell all in accordance with theforegoing object.

Other objects Will be apparent from time to time in the followingdetailed description tand discussion given in conjunction with theattached drawing -in which:

FIG. l is a perspective View of a cell that includes a compositeelectrode of this invention;

FIG. 2 shows an end view of a composite electrode of this invention; and

FIG. 3 is an end view of one form of battery that includes the novelcomposite electrodes of the invention.

It is evident, on a theoretical basis, that a zinc-bromine secondarycell should be capable of providing a high energy storage capacity. Thereactions that take place in a zinc-bromine cell 4can be indicated asfollows.

and the overall reaction is:

Zn -i-'BrzZnBrz vThe electrons associated with each zinc atom flowthrough lelectrical energy.

It can be shown that the free ener-gy of reaction of zinc and brominecan provide, theoretically, an electrical output of about 196 watt hoursper pound, and such a cell would have an open circuit voltage on theorder of about 1.8 volts at 25 C. However, since a cell cannot becomposed solely of the active components, it is evident that theelectrical output in Watt hours per pound of cell cannot be thatdetermined solely from the free energy. By Way of example, aconventional lead storage battery can provide only about 5 percent ofthe electrical output that theory indicates should Ibe available. Thelosses result primarily from the added mass required for theelectrolyte, for electrode structure, for cell structure, casing and thelike.

In constructing a cell with zinc and bromine as the negative andpositive electrodes, respectively, one of the problems is thedistribution of the bromine relative to the physical electrode thatserves as a positive terminal for the external circuit. ln the chargedstate, the bromine in the cell is in the liquid state at normalconditions of temperature and pressure and accordingly tends to seek itsown level. Nevertheless, that bro-mine should be distributed .along itselectrode to provide good reaction.

4In accordance with the present invention, the brominezinc system basedupon an aqueous zinc bromide electro- .3,328,262 Patented June 27, 1967lyte is used; from its metallic Zinc and molecular bromine are generatedat the physical electrodes during charging. Zinc and bromine reactrapidly when they contact. As already noted, bromine is liquid atordinary conditions. For purposes of this invention, the liquid bromineis adsorbed on activated charcoal. By providing this adsorption media inparticular form ialong with other cell structure, the present inventionprovides simplified cell structure, slows reaction of the Zinc andbromine and provides good contact of the Vbromine along the physicalpositive electrode.

Thus in one embodiment, the present invention provides a Acompositeelectrode comprising la shape of activated carbon. By the term shape ismeant to indicate a physical entity such Aas a hollow cylinder, a slab,or other form and to distinguish a mere mass of powders, particles,granules or the like. Activated carbon lis a well known `article ofcommerce, and generally is produced by destructive distillation ordestructive dehyd-ration of carbonaceous materials such, for example, ascoconut and other nut shells as well as coal, animal bones, lignite,paper mill waste liquor and the like. However formed, the carbon can beadmixed with `a small amount of an adhesive, shaped as desired and thenis heated to cure the adhesive. Such shapes can be obtained fromcommercial suppliers of activated carbon. The shape suitably has-opposed major surfaces, that are usually, but not necessarily,substantially parallel. On one of these surfaces there is provided asubstantially nonporous, electrically conducting coating. This coatingcan be made from carbon also, but should be dense so that it is a goodelectrical conduct-o-r for it serves as an electrode terminal in thecells. The resulting composite thus comprises a unitary structure havinga substantial Volume that adsorbs bromine and a relatively thin `coatingthat is a good electrical conductor and serves as a terminal.

The composite electrodes in accordance with this invention may include aseparator member or framework made of a material that is inert withrespect to the active components of the cell, that is electricallynonconducting but is porous so that reaction can take place upon passageof ions therethrough. There are many materials that can be used for thispurpose. Organic resins are particularly useful because they have manysuitable properties such as inertness, easy formability and strength,and are relatively lightweight, thereby not introducing unnecessaryweight. A typical material is polyvinyl chloride resin, which issuiiiciently porous to permit passage of the ionic zinc and bromine.Suitably glass mesh screening is used with the sheet of polyvinylchloride. It has been found that a composite separator as just indicatedaids in preventing internal shorting by growth of zinc dendritestherethrough as a result of charging. This member is located against themajor surface of a composite electrode that is not coated with theconducting material described above.

The invention will be described further in conjunction with the attacheddrawing. It should be understood that the details given for purposes ofillustration are not to be construed as limiting. Moreover, although thedrawings show certain specific embodiments, it should be apparent thatthe invention is not limited thereto.

Referring to the drawings, a cell or battery of the invention isprovided with a casing member 10 that, in the embodiment shown, is ofgenerally rectangular crosssection, though other shapes could as well beemployed. The casing member is composed of any suitable nonconductingmaterial such, for example, as hard rubber, or a synthetic material suchas polyethylene, polycarbonate, nylon, acrylic resin and so on.

At its top the casing is provided with a cover member 12 that may bemade of the same material, and in any event is non-conducting. Covermember 12 extends above the active area of the cell within the casingand can be considered, in part, as an expansion chamber because theactive cell components have different volumes in the charged anddischarged states. Extending upwardly -through or adjacent the topmember 12 are the electrode terminals 14 and 16. While these are shownat opposite ends for clarity, it will be apparent that both may be atthe same end of a cell or battery, as design considerations dictate.

Referring now to FIGURE 2, there is shown an end view of a compositeelectrode that includes a shape 18 of an adsorption media, for exampleactivated carbon or the like as indicated in detail hereinbefore. Alongone of its major surfaces 19 and` 20 is a coating 21 that is thinrelative to the activated carbon shape 18. The coating 21 is an integralpart of the composite electrode, and suitably is applied to one of thesurfaces of the activated carbon shape 1S and then fired thereto at atemperature sufficient to convert the coating to a substantially uniformdense thin mass. Any material desired can be used for this purpose. Forexample a mixture of conductive oxides can be used. Similarly carbon canbe applied thereto. In one satisfactory practice, the conductivematerial is admixed with a binder, and then is painted, brushed orotherwise applied to the surface and red in situ. A satisfactory coatingis provided by a mixture of carbon and a carbonizable material, forexample, a polymer of trifluorochloroethylene (Kel-F) or otherhalogenated hydrocarbon. This mixture carbonizes to a conductive,impervious (to the electrolyte) glaze or coating upon firing a thincoating of it on the activated carbon body. Thick coatings may have asmall pore volume remaining after ring. If so, the pores can be filledwith an impregnant, that may be conducting or non-conducting, with carebeing taken so that the impregnant does not unduly pass through theglazing and enter the activated charcoal region and thereby diminish itsadsorptive capacity.

A composite electrode of this invention can include a separator 24 alongthe major surface, of the activated carbon body 18, that is not coveredwith the conductive coating 21. The separator 24 can comprise a sheet ofpolyvinyl chloride and a glass mesh screen, suitably with the screenportion against the activated carbon. In any event, it is electricallynon-conducting and is suiciently porous to permit passage of ions andmolecular bromine. The separator 24 can be maintained against thesurface of the shape 18 of activated carbon by auxiliary spacingstructure (not shown), by suitable internal ribbing in the casing, by anadhesive or by any other desired manner.

A cell is made with the structure of a composite electrode and separatoras just described upon including therewith a carbon terminating platespaced from or opposed to the surface of the separator. These elementsare located in a suitable casing, and electrolyte is placed in the zonebetween the separator and the terminating plate. Leads are provided tothe carbon plate and the conducting coating on the composite electrode.Upon application of charging current, zinc is electroplated on thecarbon terminating plate while bromine is produced and is diffusedthrough the separator and into the activated carbon body Where it isadsorbed.

A greater advantage in the invention is realized in a series connectedbattery of cells including the described composite electrode, forexample in -a three cell battery. Such a battery is shown in FIG. 3 andincludes within an insulating casing member 39 three of the compositeelectrodes 40, 42 and 44, and each of which has the described conductivecoating 45, 46 and 47 on one major surface and non-conductive separators48, 49 and 50 along the other major surface. These electrodes are spacedfrom one another in the casing 39 that also includes a carbonterminating plate 54 spaced from the end composite electrode 44 oppositeor facing the separator 50 on that electrode. Terminal leads 56 and 55are then provided, one from the carbon terminating plate 54 and theother from the conducting coating 45 on the end composite electrode 40most remote from the carbon terminating plate 54. Upon adding aqueouszinc bromide 60 to the assembled cells and applying a charging current,layer 58 of zinc will plate on coatings 46 and 47 of electrodes 42 and44 as well as on the terminating plate 54. The bromine generated isadsorbed in the activated carbon portions of each of the compositeelectrodes. The battery is then ready for use.

It can be observed that the central composite electrodes 42 and 44 eachfunctions, in such a battery, as the negative electrode of one cell byvirtue of the zinc deposited on its conductive coating, and as apositive electrode in the next adjacent cell by adsorption of bromine inits activated carbon shape. The electrodeposited zinc makes goodelectrical contact with the conductive coatings and thus specialintra-cell leads are unnecessary.

In cells of the invention, activated carbon shapes having an adsorptionof about one gram or more of bromine per gram of carbon have been testedsuccessfully. By use of the principles of the invention, it has beenfound that cell and battery structure is considerably simplified. Forexample, the thin conductive coating on such electrode permits theomission of a dense carbon plate heretofore thought necessary. Since theactivated carbon distributes the bromine along the conductive coating,special framework or a distributing system are not needed. These andsimilar considerations contribute to the marked decrease in weight ofnon-active materials needed, resulting in a higher capacity per pound ofcell. Further, high drain rates are possible since diffusion of bromineWithin the electrodes does not limit the cell drain rate.

While the invention has been described in detail, it should beunderstood that changes, modifications and the like can be made withoutdeparting from its scope.

What is claimed is:

1. In a storage battery cell having active electrodes of bromine andzinc in a zinc bromide electrolyte, the improvement in combinationtherewith comprising a composite electrode of adsorptive activatedcarbon having opposed major surfaces, an electrically conducting,substantially non-porous coating bonded to one of the major surfaces, aporous, non-conducting member along the other major surface of saidshape, a dense, conductive terminating plate within the container spacedfrom the porous non-conducting member, a zinc coating on a surface ofthe terminating plate that faces the porous, non-conduct ing member, andliquid bromine adsorbed in the shape of adsorptive media.

2. In a battery cell having active electrodes of bromine and zinc and azinc .bromide electrolyte, the improvement in combination therewithcomprising a composite electrode of a shape of porous activated carbonhaving opposed major surfaces, a substantially non-porous electricallyconducting coating on one of the opposed major surfaces of the shape ofactivated carbon, and a porouselectrically non-conducting coating on theother of the opposed major surfaces of the shape of activated carbon.

3. A battery cell in accordance with claim 2 in which the non-porouselectrically conducting coating is a dense layer of carbon bonded to oneof the surfaces of the shape of activated carbon to form a unitarystructure therewith.

4. A secondary battery cell comprising a container, a shape of activatedcarbon having opposed major surfaces .disposed within said container, anelectrically conducting, substantially non-porous coating on one of themajor surfaces of the shape of activated carbon, a porous, nonconductingmember composed of an organic material and glass screen along the othermajor surfaces of said shape,

a dense, conductive terminating plate within the container spaced fromthe porous non-conducting member, a zinc coating on the electricallyconducting non-porous coating, a zinc coating on a surface of theterminating plate that faces the porous, non-conducting member, bromineadsorbed in the shape of activated carbon and an aqueous zinc bromideelectrolyte within said container.

5. A secondary battery of at least two cells comprising a container, afirst shape of adsorptive activated carbon having opposed major surfacesdisposed within said container, an electrically conducting,substantially nonporous coating on one of the major surfaces of the rstshape, forming a unitary structure therewith, a porous, non-conductingmember along the other major surface of said shape; a sec-ond shape ofactivated carbon having opposed major surfaces disposed within thecontainer, an electrically conducting, substantially non-porous coatingon a major surface of the second shape that faces said rst shape forminga unitary structure with the Second shape, a layer of zinc on thecoating on the second shape; a porous, non-conducting member along theother major surface of said second shape; a dense, conductingterminating plate within the container spaced from and opposing thenon-conducting member associated with said second shape, a layer of zincon the surface of the terminating plate opposing the non-conductingmember; liquid bromine adsorbed in the shapes of adsorptive media; alirst electrical lead to said terminating plate, a second electricallead to the electrical conducting coating on the surface of the rstshape and an aqueous zinc bromide electrolyte within the container.

6. In a battery cell having active electrodes of zinc and bromine and azinc bromide electrolyte, the improvement in combination therewithcomprising a shape of porous activated carbon having opposed majorsurfaces, la substantially non-porous electrically conducting coating onone of the opposed major surfaces of the shape of activated carbon, anda porous electrically non-conducing layer on the other of the opposedmajor surfaces, the said non-conducting layer comprising a sheet ofmicroporous resin and an interposed liquid permeable spacer member.

7. A battery cell in accordance with claim 6 wherein said non-porouselectrically conducting coating is a relatively thin layer of non-porousdense carbon.

References Cited UNITED STATES PATENTS 2,588,170 3/1952 Smith 136-22 X2,807,658 9/1957 Hatfield 136-121 X 2,907,809 10/1959 Southworth et al.136-121 3,134,698 5/1964 Neipert et al 136121 X 3,201,281 8/1965 Solomonetal 136-30 3,212,930 10/1965 Thompson et al. 136-120 X WINSTON A.DOUGLAS, Primary Examiner. A. SKAPARS, B. OHLENDORF, AssistantExaminers.

2. IN A BATTERY CELL HAVING ACTIVE ELECTRODES OF BROMINE AND ZINC AND AZINC BROMIDE ELECTROLYTE, THE IMPROVEMENT IN COMBINATION THEREWITHCOMPRISING A COMPOSITE ELECTRODE OF A SHAPE OF POROUS ACTIVATED CARBONHAVING OPPOSED MAJOR SURFACES, A SUBSTANTIALLY NON-POROUS ELECTRICALLYCONDUCTING COATING ON ONE OF THE OPPOSED MAJOR SURFACES OF THE SHAPE OFACTIVATED CARBON, AND A POROUS ELECTRICALLY NON-CONDUCTING COATING ONTHE OTHER OF THE OPPOSED MAJOR SURFACES OF THE SHAPE OF ACTIVATEDCARBON.